With the development in communication technology, a terminal such as a smartphone that has a communication function is in widespread use. Meanwhile, societal demands on reducing power consumption of terminals are increasing due to concern for global warming. Further, for a battery-powered terminal such as a smartphone, there is a need for reducing power consumption of the terminal from the standpoint of the convenience by increasing run time thereof.
In response to the demands for reducing power consumption, a framework named ACPI (Advanced Configuration and Power Interface) for power supply control is being proposed. According to the above, a state named “S3” is defined. The “S3” is a state that is called “Suspend to RAM.” In the “S3” state, a value in a register of a CPU is written out in a main memory, and feeding of power to the CPU, a bus, and bus devices are stopped while the main memory is kept in an energized state. A terminal in the “S3” state cannot carry out an operation, but power consumption thereof is smaller than in an “S0” state (an operating state). Further, when the terminal returns to the “S0” state from the “S3” state, the terminal can return to a state prior to transitioning to the “S3” state. Therefore, it is more convenient than a cold boot.
Further, there exists another technique: in a case where there is neither receiving nor transmitting packet for a predetermined period of time in a wireless LAN terminal, information that is necessary to transmit data to a connected access point is stored in the terminal, and feeding of power to a communication circuit is stopped. When a transmitting packet is generated, power is fed to the communication circuit, and the packet is transmitted to the access point having been connected to previously using the stored information without carrying out a connecting procedure. In this way, by omitting the procedure to connect to the access point, a delay that is required for transmitting a packet after power is fed to a communication unit is reduced.
In recent years, services called Web services or cloud services have been in widespread use. For example, Gmail by Google Incorporated or the like can be cited. With Gmail, mail data are present on a server, and by accessing them from a Web browser, a list of received mail and content of selected mail are displayed without using a dedicated mail application. When assuming such a service, from the standpoint of power consumption, it is desirable that a local terminal stops feeding power to a wireless LAN communication unit each time necessary data are received and feeds power to the wireless LAN communication unit only in a case where communication becomes necessary. However, a delay from when feeding of power to the wireless LAN communication unit is started until a packet can be transmitted is large, and the convenience for a user is lost.
On the contrary to this, there exists a method in which feeding of power to the wireless LAN communication unit is stopped while retaining information on the connected access point. When transmission of a packet becomes necessary, power is fed to the wireless LAN communication unit and the packet is transmitted to the access point using the retained access point information.
However, if a state where feeding of power to the wireless LAN communication unit is stopped lasts long, there is a possibility that the access point determines that the terminal has disappeared and discards association information. At this time, if the communication terminal starts feeding power to a wireless LAN interface to transmit a packet, the transmitted packet is discarded at the access point. Then, after a predetermined period of time, the communication terminal retransmits the packet for a predetermine number of times. In this way, the communication terminal fails to realize that the access point has discarded the association, and there exists a problem in that duration in which a packet cannot be transmitted increases.
In this way, there has been an issue in that if feeding of power to the wireless LAN communication unit is stopped for a power saving state, a delay until transmission of a packet becomes possible is large and thus the convenience for a user is lost.